Repairs to a heat exchanger tube often require the plugging of the ends when part of the tube becomes corroded or begins to leak into the surrounding medium. However, before a tube end can be plugged, it is necessary to puncture or server the body of the tube to prevent liquids from being trapped within the tube. If this is not done, there would be a subsequent pressure build-up inside the plugged tubes and eventually the plug would blow out.
Due to the nature of many types of heat exchangers, access to these tubes is usually restricted; consequently they must be cut from the inside. A common procedure for severing tubes to be plugged used a mechanical fly cutter. This tool consists of a specially-designed pair of cutting bits enclosed within a cutter body. For normal cutting operations the tool is inserted into the tube to be cut, the cutter bits are extended from within the tool by a retractable mandrel, and then the bits are spun in a 360.degree. circle by an air motor. When the bits are fully extended, the tube will be completely severed. Afterwards, the mandrel is retracted causing the bits to retract within the cutter body and as a result the tool may be removed.
There are several disadvantages to this procedure. Using the mechanical fly cutter is a slow and sometimes involved process that requires an air motor and an associated compressor. Additionally, once the tube has been severed, it is free to vibrate and damage the surrounding tubes which may, in turn, necessitate their repair as well. The remaining disadvantage of the device is that metal shavings and dirt enter the inside of the cutter body where the bits extend, causing these bits to lock in the extended position. Once this occurs, it is impossible to remove the cutter without damaging or breaking the bits; if so, then replacement is necessary. Other tools are also presently available for puncturing tubes to be plugged, but there are disadvantages to these tubes as well. They are mechanical and require a great deal of force to penetrate a heavy-walled tube, and when smaller tubes are to be punctured, the stresses involved can cause the tool to bend or break.
The present invention is unique in that it is lighter, involves fewer parts, has a lower cost, and punctures a hole that relieves the internal pressure of the tube without damaging any surrounding tubes.